1. Field
The present description relates in general to the field of inductor-based switching-mode direct current-to-direct current (DC-DC) converters and more specifically to a DC-DC converter of that kind operating in a discontinuous conduction mode (DCM).
2. Description of the Related Art
Inductive DC-DC converters are typically characterized by long times in which the inductor current falls down. If the available power is very low, the converter has to work in discontinuous conduction mode, which means that for a certain interval of time the inductor current remains equal to zero. In order to prevent a current to an energy storage element connected to the DC-DC converter from becoming negative, that is, the DC-DC converter circuit takes current from that energy storage element, an inductor zero current crossing condition has to be detected.
An exemplary DC-DC converter operating in a discontinuous mode is described in U.S. Pat. No. 6,847,197, which comprises an electronic circuit for detecting a zero current condition flowing through an inductor, the entire contents of which are herein incorporated by reference. In such a DC-DC converter an inductor is charged by coupling the inductor to a voltage source for a predetermined amount of time; thereafter, the inductor is discharged by coupling the inductor to a ground until the current flowing through the inductor equals zero; and a method for detecting a zero current flowing through the inductor includes coupling the inductor to a transistor and comparing the output of that transistor to a transistor coupled to ground.
Another example of an inductor-based DC-DC converter is described in EP Patent Application 2 251 966 A1, which comprises a switch control circuit, and a switch controllable to cause the DC to DC converter to alternate between a magnetization phase in which an inductor current in the inductive component increases, and a demagnetization phase in which the inductor current decreases, the entire contents of which are herein incorporated by reference. The switch control circuit compares an inductor current to an intermediate threshold below a maximum inductor current, and compares an output voltage to a voltage threshold. The converter switches from the demagnetization phase to the magnetization phase when the inductor current has dropped below the intermediate threshold, and dependent on the output of the second comparator. This intermediate current threshold enables the conduction mode to be continuous at high loads and discontinuous at light loads.
A problem with the current state of the art inductor-based DC-DC converters is its speed, power consumption and/or precision performance in, for example, low power applications, e.g. in which the input available power can vary from a few microwatts to several milliwatts. The control circuit used in such inductor-based DC-DC converters needs to turn on and off the switches at the right time, and to improve the precision, speed and/or dynamic range in such control circuits there is still a need for high power consumption.